Incandescent lamp bulb



H. B. DONLEY Sept. 18, 1928.

INCANDES CENT LAMP BULB Filed May 1 192 Patented Sept. 18, 1928.-

UNITED STATES 1,684,949 PATENT OFFICE.

HAROLD B. DONLEY, OF COLUMBUS, OHI O, ASSIGNOR OF ONE-THIRD TO W; HERBERT BBETZLAIF, OI INDIANAPOLIS, INDIANA.

INCANDESCENT LAMP BULB.

Application filed May 1, 1926. Serial No. 196,096.

This invention relates to improvements in lamps and bulbs, and particularly to incandescent lamp bulbs used in automobile'lighting devices, or other devices for the projection of light. a

An object of the, invention is to eliminate or control that part of the glare or stray light projected from a reflector using an incandescent lamp bulb as its light source, which is produced by internal reflection of the lighted filament from the glass walls of said bulb.-

VVhen a lamp bulb is positioned with its lighted filament in the focal point of a parabolic reflector, or other similar mirror, a

i major beam of comparatively high intensity is projected. However, with a glass bulb around the filament there is a certain portion of the light from the filament that is reflected back from the interior glass wall of the bulb. If the front of the bulb is spherical, which is usual, and the filament occupies a center of the bulb, this light will be reflected by the spherical portion and pass back theoretically substantially through the same point from which it emanated. Thus if the filament located in the focal point of the reflector and the secondary image of hght C0111- ciding with the main filament, the secondary beam from the reflector will coincide with so the major beam. Considered, practicall however, this is really an impossibility 1n the production and manufacture of vehicle lamp bulbs. If the filament is not 1n the true center of the spherical portion of the bulb but still in the focal point of the reflector, there will be two beams projected from the reflector, one'of high intensity, which is the normal beam, and a secondary beam of lower intensity. Assuming the front por- 40 tion of the bulb to be a sphere, and the filament thereof located out of the center of the sphere, then the internal reflected rays 'Wlll take vagrant or uncontrolled paths of projection. These stray or vagrant rays, 1m- 46 pinging the reflector, produce a secondary beam of comparatively low intensity, but still intense enough to be obnoxious to an approaching observer or motorist.

The present invention provides means for no compensating for this irregularity 1n manufacture by so designing the shape of the front of the bulb that the internal reflected images are reflected to some neutral point where they will not impinge the reflector, while the .within the bulb 5 is the usual reflected images from the other portions of the bulb are well disseminated.

With these and other objects in view, as i lgurc 3 is a diagrammatic View showing the paths of light pro ectlon from a bulb having a. spherical forward wall,

Figure 4 is'a similar view of a slightly modified form of bulb capable of carrying out the features of the present invention.

Referring more particularly to the drawings the numeral 1 designates in its entirety an improved lamp comprising the present invention. In the form thereof disclosed especially in Figures 1 and 2 the lamp comprises a customary base 2, by which the same is mounted in a receiving and supporting socket 3 located in the principal axis of an associated parabolic reflector 4, the latter being of the usual type provided in connection with automobile illuminating devices.

The present invention is addressed particularly to the specific design or formation of the glass bulb 5 of the lamp, and, as shown, this bulb is in its process of manufacture shaped to provide a conoidal body portion 6, the smaller end of which being joined as usual with the base 2, and the outer or'larger end thereof being terminated in a front walL7 which in this instance is of substantially true elliptical form, as shown by the construction lines 8, disclosed in Figure 1. Arranged filament, or filaments 9, disposed to occupy substantially the forward focus 10 of the elliptical wall 7.

By reference to Figure 1 it will be observed that by the elliptical formation of the wall 7 the internally reflected light of low intensity evolved in'the bulb will, upon reflection from the wall 7, be directed backwardly or rearthe bulb, can not reach the reflector 4 but are neutralized or eliminated by being concentrated upon the lamp base.

As shown in Figure 3 these internally reflected rays, which are the premature source of lamp glare, when reflected within a lamp bulb 12 having a spherical front wall, are reflected outwardly through the walls of the bulb 12 so as to impinge upon the surface of the associated reflector, with the result that I a after striking the surface of the reflector,

these secondary rays are released from the lighting device in scattered, diverse paths, and instead of following the path of main light projection, are distributed to the sides of the illuminating device so as to fall into undesired areas or zones of illumination. Use and experimentation has disclosed that it is these uncontrolled secondary rays that produce to a very large extent the'obnoxious glare emanating from the usual vehicle illuminating device.

It will be observed that by the provision of the present invention these secondary rays are neutralized, compensated for or eliminated so far as regards light projection from a vehicle lamp. While the front wall 7 of the bulb has been shown and specifically described as being of true elliptical form, it is obvious that this exact shape need not be strictly followed, in that it is within the scope of t e inventionv to form this wall in any shape, whether a regular or an irregular curve, just so long as the internally reflected light is directed into the confines or area of the lamp wherein the rays do not impinge upon an associated reflector. Such a shape has been disclosed in Figure 4 wherein the front wall 13 of the bulb is in the form of an irregular curve but capable of directing the internally reflected rays back into the'base of the bulb.

What is claimed is:

In a lamp, a base, a glass bulb projecting forwardly from said base and including a conoidal body portion and a substantially elliptical front wall, the body portion and the said wall being of uniform thickness throughout, an unobstructed filament positioned with- ,in said bulb and so placed with respect to the elliptical front wall thereof that the internally reflected light rays from said wall are thrown back into the area of the lamp base.

In testimony whereof I aflix my signature.

HAROLD B. DONLEY. 

